The present invention relates to a copier, facsimile transceiver, printer or similar image forming equipment having an image carrier, a developing device, and a cleaning device.
One of predominant types of image forming equipment available today forms a latent image electrostatically on an image carrier such as a photoconductive element, develops the latent image by a developing device to produce a toner image, transfers the toner image to a recording medium, and removes toner particles which remain on the image carrier after the image transfer by a cleaning device. In this type of image forming equipment, the developing device needs maintenance including the supply of toner and replacement of developer, while the cleaning device needs maintenance including the disposal of collected or waste toner. These two kinds of maintenance are effected at intervals which depend on the capacity of the equipment; the smaller the size of the equipment, the shorter the intervals. Handling a toner, for example, is awkward since the toner is apt to smear the operators hands, clothing and ambience. In the light of this, a disposable process cartridge having a developing device, cleaning device and other devices implementing the image forming process integrally therein has been proposed. A disposable developing device and a disposable cleaning device have also been proposed in the past. Although these disposal schemes may be useful for operators, they are contradictory to the current trend toward the reuse of resources since all the component parts including those which are still usable have to be discarded.
To postpone the time for disposal, two image forming units each having a developing device and a cleaning device may be installed in an image forming apparatus symmetrically to each other with respect to the axis of a photoconductive drum, or image carrier, as disclosed in Japanese Patent Laid-Open Publication No. 31865/1987. In such apparatus, one of the two image forming units is located in the developing position of the image carrier while the other is located in the cleaning position of the same. The image forming unit located in the developing position and the image forming unit located in the cleaning position have respectively the developing device and the cleaning device thereof rendered effective, i.e., only one developing device and only one cleaning device are operated at a time. When the developer stored in the developing device of one image forming unit deteriorates or when the ability of the cleaning device is lowered, the two units are removed from the equipment, replaced with each other, and then mounted again on the apparatus. Then, the other developing device and the other cleaning device which are fresh are used.
The problem with the above-described interchangeable unit approach is that the developing device of one image forming unit and the cleaning device of the other image forming unit are not operated while the others are operated, wasting substantial part of the limited space available in the apparatus. Further, the toner collected by the cleaning device of each image forming unit is simply discarded. This is undesirable from the standpoint of effective use of toner.